Foundry mold coating



United States Patent 3,219,465 FOUNDRY MOLD COATING Phillip F. Herkimer,Royal Oak, Neil M. Lottridge, In, Warren, and Douglas G. McCullough,Rochester, Mich., assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware No Drawing. Filed May 26, 1961, Ser.No. 112,755

7 Claims. (Cl. 106-3823) This invention relates to a Coatingcomposition, which when applied to foundry sand mold and core surfaces,functions as an effective anti-veining coating to appreciably improvethe surface finish of castings produced by the use of such a mold orcore. In addition, the fluidity of molten casting metals, such as graycast iron, malleable iron, spheroidal graphite cast iron, aluminumalloys and magnesium alloys, poured into contact with the coated mold orcore is significantly increased. More specifically, the inventionpertains to a foundry mold or core wash containing finely divided mica,corn cereal and wood flour suspended in a liquid carrier.

In the past it was frequently impossible to successfully cast some thinsections of the aforementioned metals except by superheating the castingmetal, preheating the mold and/or substantially increasing themetallostatic pressure. Obviously it is desirable to eliminate theseprocedures. A principal object of the present invention, therefore, isto provide a coating for foundry sand molds and cores which materiallyincreases the fluidity of molten casting metals contacting such moldsand cores without employing superheat, preheated molds or undersirablyhigh metallostatic pressures. As a consequence, sound castings of verythin section can be formed by conventional procedures. The termfluidity, as used herein, refers to that property of molten castingmetal in contact with a mold which allows the metal to flow into themold and fill it before solidification obstructs further flow of themetal.

The above and other objects of this invention are attained with afoundry mold and core coating comprising a slurry of mica or vermiculitepowder, powdered corn cereal, wood flour and a liquid vehicle, such asmethyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, a chlorinatedhydrocarbon, commercial mineral spirits or water. Small amounts of asuspension agent, a binder, a low-foaming, nonionic wetting agent and anantifermentation agent also may be beneficially included in the slurry.The coating composition thus provided is relatively inexpensive and canbe readily applied to the mold surfaces by conventional means, such asspraying, dipping or brushing.

It will be understood that the term mold, as hereinafte'r generallyemployed, means a casting form which includes both molds and cores, thisinvention not being limited to the former. Likewise, the word sand" isused in its generic sense and is not restricted to silica particles.

This mica powder should constitute about 70% to 95% by weight of thesolids content of the coating composition, while the amount of corncereal to be used may vary from approximately 2% to of the weight of thesolids. In general, the wood flour content can range between about 1%and 12%. The preferred solids composition includes approximately 75% to90% by weight of mica powder, 4% to 14% by weight of corn cereal and 3%to 8% by weight of wood flour. For most applications the particle sizesof these powdered constituents should be between 80 and 325 mesh,although finer powders may be used.

The presence of the corn cereal permits the slurry to be handled moreconveniently than the mold coatings ice heretobefore proposed for thesame purpose. This is possible because of the lower liquid-to-solidsratio permissible with the new coating composition and the resultantfaster drying time. The suspension is easier to apply to molds andcores, particularly by dipping, and its superior consistency reduces theamount of coating material lost due to dripping. Also, a smaller amountof wetting agent can be employed, and the wet-ting agent may beeliminated entirely for some applications. In addition, the presence ofcorn cereal permits a reduction in wood floor content with a consequentdecrease in the amount of mold gas generated during pouring of themolten casting metal. As a result, the castings are sounder and lessporous.

The coating slurry preferably is applied to green sand molds by aspraying procedure, and when this is done it is advantageous to mix theabove-described powdered constituents with a volatile organic liquid,such as commercial methyl alcohol, ethyl alcohol, isopropyl alcohol,toluene, a chlorinated hydrocarbon or naphthol spirits. A slurry of thistype also can be used to spray baked sand molds and cores, or water maybe employed as a less expensive carrier if the molds and cores aresubsequently reheated to dry the coating. Of course, in the case ofbaked sand cores, it is convenient to apply a water slurry by a dippingoperation. When alcohol is used as the liquid carrier, any excessalcohol can be readily burned off.

In order to obtain a proper dispersion of the coating composition on themold surfaces when a water suspension is used in a dipping operation, itis desirable to include a wetting agent. A low-foaming, nonionic wettingagent is preferred. Examples of such'a wetting agent are those availableunder the trade names Ir-62 Pluronic and L-64 Pluronic. Likewise theadherence of the coating to the mold may be further improved for someapplications by adding a thickener or binder to the slurry. Methylcellulose has proved to be a satisfactory water thickener, but othershort-chained alkyl celluloses, such as ethyl cellulose, butyl celluloseand propyl cellulose, may be employed. Ceron N-4S also has proved to bean excellent suspension agent and binder. This water-soluble derivativeof wheat starch is a nonionic, etherified polymeric carbohydrate. Awater thickener of this type appreciably improves the dipping characteristics of the slurry and increases the hardness and durability of thedried coating.

The amount of liquid carrier used should be sufficient to provide aslurry which can be readily applied to the mold. If it is desired to dipthe mold, the ratio of the liquid carrier to the solids content of thecoating composition may vary between approximately 4 to 1 and 10 to 1.On the other hand, this ratio may be as low as 2 to 1 for spraycoatings. Thus it will be seen that the amount of liquid in the slurrymay constitute about 65% to 91% of the total weight of the slurry, but acoating having a water content of approximately to is generallypreferred.

When a wetting agent is used in the mixture, the addition of 0.5 gram to2 grams of this material to 500 milliliters of slurry has proved to beadequate. In fact, as little as about 0.1% by weight of wetting agentimproves the coating composition, and as much as 1% wetting agentSometimes may be used to advantage. Dipping characteristics and slurrysuspension are further improved when the composition contains Ceron N-4Sin an amount equal to about 1% to 5% by Weight of the solids in thecomposition. Approximately 2 to 3 grams of this material added to 500milliliters of the slurry has proved to be particularly effective. Whenmethyl 3 cellulose is used it preferably constitutes approximately 0.2%to 1% by weight of the solids in the slurry.

In addition to the above-described constituents, urea formaldehyde orother soluble resins may be included agitated. In general, it isdesirable to maintain the pH of the water between 5 and 7 because someof the solid constituents appear to disperse somewhat better in waterwhich is slightly acidic. If urea formaldehyde is to be in the slurry,particularly if a wetting agent is to be 5 included in the coating, itis the last constituent added to used, to further increase the hardnessand durability the slurry. The coating composition should be stirred ofthe dried coating. A relatively small amount of for several minutes andnot used for at least four hours. other binder materials also may beadded to the slurry N y it is pp to the Casting-defining surfaces of toimprove the adhesion of the coating to the sand mold t ld at r mmperatureif the binder is soluble in the liquid carrier. Among 10 Thefollowing table lists specific examples of coating these binding agentsare thermoplastic resins such as compositions prepared in accordancewith the present inpolyvinyl chloride, vinylidene chloride, polyvinylalcohol vention:

Example Example Example Example Example I II I IV V Water 100 gaL. 40gal 500ml 800 m1. Isopropyl alcohol 300 m Mica powder (-160 mesh)100111... 58.5 lb... 85 gm. Corn cereal 11lb. 3.411)--.. 10 gm. Woodflour (-80 mesh) 5.6 lb 3.4 lb 5gm. Wetting agent 300 grn 401111.-.. 1lgrn. Ceron N-4S thickener 41b"... 1.67 lb.-. 4 gm. Calcined clayCuSO4-5H2O 0.241b. 60gm 02gm Phenol-formaldehyde resin and polyvinylacetate, and thermosetting resins such as Each of the above coatingcompositions had excellent phenolformaldehyde and melamine formaldehyde.Of dipping characteristics, dried in a reasonable period of course,Various other binders besides the polymeric vinyl time and was hard anddurable upon drying. In addiand phenolic resins can be employed, Forexample, tion, the coatings substantially reduced Chill in thinseclinseed oil and certain clays, such as bentonite cla tions andmaterially aided in the cleanup of the castings. are u eful as bi d timt Furthermore, use of these coatings as compared with When a coatingcomposition having mineral spirits or currently commercially used greenSand mold p y and al h l as th carrier i t b applied b Spraying, corewashes significantly decreased metal penetration into tainthermoplastic, lignin-type resinous materials derived e meld and/01:Ceres, thereby improving the Surface from wood and containing bothmethoxyl and hydroxyl finlsh 0f the ngs in h ir a aSt eonditlon. groupshave proved to be useful as additional binders if W ry Sand test moldswere coated with the aboveincluded in the slurry in small amounts. Suchmaterials described Shlffies, the fluidity of y Cast iron, malleable maybe obtained from a variety of wood products, includiron and spheroidal gp Cast iron Poured at normal i d t waste li f h paper i d d castingtemperatures into these molds was increased more chips, etc., byphysical and/or chemical treatment. Illusthan 100% as comp With SimilarmeldsWhieh W r trative of one type of thermoplastic resinous material isuneoated- T i y 0f the molten m te-1 1n themolds a substantiallygasoline-insoluble resinous material obwas deteflhlhed y means of adouble SPITel fluldlty test tained by extracting a resinous wood with acoal tar e in Which One pir l i a ed With the mold wash hydrocarbon,removing the hydrocarbon by evaporation, Whlle the other remainsuncoated, both being fed y leaving a residue comprising a mixture ofwood rosin h Same Pellflhg basin and down P e- The relative andthermoplastic resinous material, and extracting the dlstahces the metelf l in Spiral IS a e Of rosin with a petroleum hydrocarbon, leaving athermothe Improvement 1h h y- This e e de$1gI1 1I1d plastic resinousmaterial. Such a product is available the Procedure for using it aredescribed In Transa tlons under the trade name Vinsol. of the AmericanFoundrymens Society, volume 67.

Of course, more than one binder may be used in the Pages 496 to coatingcomposition, but the total binder content in ad- Tests have beenconducted on Castings of y iron, dition to the corn cereal normallyshould not constitute malleable iron, spheroidal g p Cast iron andumimore than about 5% of the weight of the solids in the hum alleysWhich Were f m d in molds coated in acti t i l, E 05% b Weight f thddicordance with this invention. As a result of these tests, tionalbinder in the coating causes it to adhere more it Was found that thesemetals Could he Successfully east strongly to the mold. in thin sectionsby using the above-described mold wash A water Slurry t i i d fl comcereal and that the resultant castings all had exceptionally high and/or Ceron N-4S will ferment after a relatively short ultimate tensile hgd nesstime, thereby reducing the bonding action of the Ceron p thlekseetlons of gray iron cast N 4S a d th com l, H we h fo d it d in greensand mold portions coated with this mold wash sirable to include a smallamount of an antifermentation were compared with g y Specimens of th ameagent to retard the growth of bacteria. Copper sulfate, composition fheh thlek se lons cast in the potassium chromate, sodium chromate,sodium hypersame molds without a The f I1 th chlorate, urea formaldehydeand paraformaldehyde all h thlek Seetlons had pp y hlghef llltlmate haveproved to be useful for this purpose. Shelf life e g an ardness than thecast iron in the A6- of an aqueous slurry has been increased fromapproxih th lek Seetlohs- {\tteInPtS to Cast -ln hl k seemately 3 daysto more than 2 we k because f th titlons without first coatlng thesurfaces of the mold cavities b t i l ti f h an ddi i were unsuccessfulbecause the molten metal would not The above-described coating slurrymay be prepared P p y feed i fill t e narrow mold cavities. in thefollowing manner: The dry materials, such as the The gray cast lI'OIlWhlCh did feed lnto these /8-111Ch mica, com cereal d d flour, arepreferably fi t cavities of uncoated molds was chilled, and hence theseblended to powder form. Next, the wetting agent is Peftlehs 0f theCastlhgs were hard, brlttle d unmaadded to the desired amount of water,assuming an chinable. Green sand molds, each having two cavities aqueousslurry is to be used; and the blended solids are o r inches Wide and 18inches l g, With ns 43' introduced slowly into the slurry while thelatter is being inch and -inch deep, were used 1n these tests.

It was further noted that the microstructure of the /sinch thicksections of gray iron castings poured into the coated mold portions wasslightly more refined than the microstructure of gray iron specimenscast into the A inch thick uncoated portions of the same mold. Noprimary carbide was evident in either section.

Additional tests under production conditions also showed that use of thenew mold coating improved the surface finish of the castings anddecreased the incidence of veining, thus greatly reducing the amount oflabor necessary in cleaning operations. Moreover, the coating preventedmisruns and cold shuts. As a consequence, leakers were eliminated, andthe scrap rate due to such defects was lowered from approximately 9% toless than 1%. Furthermore, the mold coating described herein has arelatively short drying time and a wide drying temperature range. It maybe dried at a temperature up to approximately 500 F. without blisteringand coatings on port cores for gasoline engine cylinder head castingswere dried in only about five minutes at 500 F. This coating compositionalso has good dipping characteristics and is uniform in thickness bothbefore and after drying, as Well as being relatively inexpensive to use.

While our invention has been described by means of certain specificexamples, it is to be understood that its scope is not to be limitedthereby except as defined by the following claims.

We claim:

1. A slurry for coating casting-defining surfaces of foundry sand molds,said slurry being formed from a dry blend consisting essentially ofabout 70% to 95% by weight of mica powder, about 2% to 20% by weight ofcorn cereal and about 1% to 12% by weight of wood flour to which hasbeen added a liquid carrier in an amount sufficient to constitute about65% to 91% of the total weight of said slurry.

2. A coating slurry for application to casting-defining surfaces of afoundry mold, said slurry consisting essentially of a liquid carrier anda dry blend, said dry blend consisting essentially of about 75% to 90%by weight of mica powder, about 4% to 14% by weight of corn cereal andabout 3% to 8% by weight of wood fiour, said liquid carrier beingselected from the group consisting of methyl alcohol, ethyl alcohol,isopropyl alcohol, toluene, mineral spirits, naphthol spirits and waterin proportions such that said dry blend constitutes approximately 15% to25% of the total weight of said slurry.

3. A coating slurry for application to casting-defining surfaces of afoundry mold, said slurry consisting essentially of about 65% to 91% byweight of water and about 9% to 35% by weight of a dry blend, said dryblend consisting essentially of about 70% to 95% by weight of micapowder, about 2% to 20% by weight of corn cereal, about 1% to 12% byweight of wood flour and about 1% t by weight of a nonionic, etherifiedpolymeric carbohydrate, the particle sizes of said mica powder, corncereal and wood flour not exceeding approximately 80 mesh, said slurrycontaining about 0.1% to 1% by weight of Wetting agent.

4. A coating composition for application to castingdefining surfaces ofa foundry sand mold, said composition consisting essentially of asuspension of a powder in water, said powder consisting essentially of,by weight, about 75% to 90% mica, 4% to 14% corn cereal and 3% to 8%wood fiour, said suspension containing a polymeric organic binder in anamount not in excess of about 10% of the weight of said powder.

5. A foundry mold for use in producing a metal casting having at leastone thin section, said mold being formed of foundry sand and havingcasting-defining surfaces provided with a thin coating consistingessentially of about to 95% by weight of mica, 2% to 20% by weight ofcorn cereal and 1% to 12% by Weight of wood flour.

6. A foundry mold for use in producing a metal casting having at leastone thin section, said mold being formed of foundry sand and havingcasting-defining surfaces provided with a thin coating formed byapplying to said surfaces a slurry consisting essentially of a liquidcarrier and a dry blend, said dry blend consisting essentially of about70% to 95% by weight of mica powder, about 2% to 20% by weight of corncereal, about 1% to 12% by weight of wood flour and about 1% to 5% byweight of polymeric carbohydrate and a small amount of anantifermentation agent, the amount of liquid carrier being sufficient toconstitute about 65% to 91% of the total weight of the slurry.

7. A foundry mold for use in producing a metal casting having at leastone thin section, said mold being formed of foundry sand and havingcasting-defining sur faces provided with a thin coating formed byapplying to said surfaces a slurry consisting essentially of a dry blendsuspended in a liquid carrier, said dry blend consisting essentially ofabout to by weight, of mica powder, about 4% to 14%, by weight, of corncereal, about 3% to 8%, by weight, of wood flour, the amount of liquidcarrier in said slurry being sufiicient to constitute about 65% to 91%of the total weight of said slurry, said liquid carrier being selectedfrom the group consisting of methyl alcohol, ethyl alcohol, isopropylalcohol, toluene, mineral spirits, naphthol spirits and water.

References Cited by the Examiner UNITED STATES PATENTS 1,858,083 5/1932Goldsmith 10638.24 2,735,814 2/1956 Hodson et al 10638.24 2,798,8177/1957 Lund 10638.23 3,115,414 12/1963 Lottridge et a1. 10638.23

OTHER REFERENCES Websters New International Dictionary, 2nd Edition, G.and L. Merriam Company, Springfield, Massachusetts, 1959, (page 725).

ALEXANDER H. BRODMERKEL, Primary Examiner.

JOHN R. SPECK, LESLIE H. GASTON, Examiners.

1. A SLURRY FOR COATING CASTING-DEFINING SURFACES OF FOUNDRY SAND MOLDS,SAID SLURRY BEING FORMED FROOM A DRY BLEND CONSISTING ESSENTIALLY OFABOUT 70% TO 95% BY WEIGHT OF MICA POWER, ABOUT 2% TO 20% BY WEIGHT OFCORN CEREAL AND ABOUT 1% TO 12% BY WEIGHT OF WOOD FLOUR TO WHICH HASBEEN ADDED A LIQUID CARRIER IN AN AMOUNT SUFFICIENT TO CONSTITUTE ABOUT65% TO 91% OF THE TOTAL WEIGHT OF SAID SLURRY.